> "YYYY-MM-DD hh:mm:ss"

> It is human-friendly and computer-friendly at the same time.

It's not shell-friendly, because of the space. The shell being an interface between humans and the computer, this takes a chunk out of it being human-friendly and computer-friendly. You'll have to worry about quoting the thing, involve messing with IFS when making arrays of the things, extract both pieces out of text columns aligned with spaces, awk's NF wouldn't correspond with number of fields anymore, etc. Would make timestamps unnecessarily annoying to interact with. Better to at least make it an underscore. Still quite readable.